1. Field of the Invention
The present invention relates to an apparatus for inspecting component-mounted electronic devices. More particularly, the invention relates to an apparatus for inspecting a printed circuit board (hereinafter referred to as "substrate") mounted or equipped with electronic components (hereinafter referred to as "packages"), the apparatus being capable of automatically discriminating between the types or species of the components and determining whether the components are mounted in the correct positions on the substrate.
2. Description of the Prior Art
As the packaged substrate inspecting apparatus (also known as the package inspecting system) for inspecting the packaged electronic/electric device equipped with electlic and/or electronic parts by means of a mounter or the like apparatus, there has been heretofore known such a structure as shown schematically in FIG. 1 of the accompanying drawings.
As will be seen in this figure, the package substrate inspecting apparatus or system is composed of a television camera (referred to simply as TV camera) 3 for picking up an image (also referred to as imaging) of a substrate 2b on which electronic/electric parts are mounted or packaged and which is to be inspected and a reference packaged substrate 2a (which serves as a reference or standard substrate) for inspection, a memory 4 unit in which the image (reference image) of the reference packaged substrate 2a picked up by the TV imaging camera 3, a comparison/decision circuit 5 for comparing the data of image (image to be examined) of the packaged substrate 2b under inspection available from the TV camera 3 with the reference image data read out from the memory 4 for making decision as to whether all requisite parts 1b are mounted on the packaged substrate 2b under test or whether any of the mounted parts are displaced or dislocated from the respective correct positions, and a display unit 6 for displaying the results of the decision issued by the comparison/decision circuit 5.
The prior art packaged substrate inspecting apparatus of the type outlined above is so designed as to compare simply the position of the part 1a mounted on the standard or reference packaged substrate 2a with that of the part 1b mounted on the printed substrate under inspection, wherein upon detection of positional incoincidence between these parts 1a and 1b, it is determined that the part 1b is not mounted correctly. In this way, the decision of failure in mounting of the part is always issued whenever the part mounted on the packaged substrate 2b under test is dislocated from the standard or correct position 7 (the position indicated by the part 1a on the standard substrate 2a), as is illustrated in FIG. 2 of the accompanying drawings, even if the part 1b on the substrate 2b under test is so positioned that electrodes thereof can be electrically connected to the respective mounting lands 9b, as is shown in FIG. 3.
In order to evade the inconvenience mentioned above, it is conceivable that a permissible range 8 within which the part 1b mounted on the substrate is allowed to be positionally deviated more or less is previously established on the basis of the correct or standard position of the part 1b, wherein so far as the part 1b is found to be located within the permissible range, it is decided that the part 1b is mounted correctly. In that case, however, the permissible range 8 has to be prepared for each part 1b in dependence on the species thereof, because the geometrical factor such as profile or outline of the permissible range 8 will vary from one to another part. By way of example, the dimension as well as geometry of the permissible range 8 for a transistor having three electrodes will differ from that for a resistor or capacitor having two electrodes. Consequently, very troublesome and time consuming procedure will be involved in preparing and registering a great variety of data concerning the permissible ranges 8 of various sizes and profiles in the inspection system.
Besides, experience shows that the circuit pattern printed on the substrate slightly differ from one to another even though a same patterning mask is employed. Consequently, even when the part 1b is correctly mounted relative to the land 9 of the substrate 2a, there arises a possibility that decision of failure in mounting will be issued when the position of the land 9 on the substrate 2a under test differs from that of the corresponding land on the standard substrate 2a, i.e. when the land position 9a and the part position 10a on the standard substrate 2a of which data have been previously loaded in the memory unit 4 are deviated from the land position 9b and the part position 10b obtained by imaging the packaged substrate 2b under test with the TV camera 3, as illustrated in FIG. 3, notwithstanding of the fact that the part position 10b actually lies in a correct positional relationship with the land position 9b, giving rise to another problem.